Sign in →

Test ID: CDG Carbohydrate Deficient Transferrin for Congenital Disorders of Glycosylation, Serum

Reporting Name


Useful For

Screening for congenital disorders of glycosylation


This test is not useful for screening patients for chronic alcohol abuse.

Specimen Type


Ordering Guidance

This test is for congenital disorders of glycosylation. If the ordering provider is looking for evaluation of alcohol abuse, order CDTA / Carbohydrate Deficient Transferrin, Adult, Serum.


If either PMM2-CDG (CDG-Ia) or MPI-CDG (CDG-Ib) is suspected, order PMMIL / Phosphomannomutase and Phosphomannose Isomerase, Leukocytes.

Necessary Information

1. Patient's age is required.

2. Reason for testing is required.

Specimen Required

Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 0.1 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.

Specimen Minimum Volume

0.05 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Frozen (preferred) 45 days
  Refrigerated  28 days
  Ambient  7 days

Reference Values





Transferrin mono-oligo/di-oligo ratio




Transferrin A-oligo/di-oligo ratio




Transferrin tri-sialo/di-oligo ratio




Apo CIII-1/Apo CIII-2 ratio




Apo CIII-0/Apo CIII-2 ratio





Day(s) Performed

Monday, Thursday

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
CDG CDG, S 90417-7


Result ID Test Result Name Result LOINC Value
BG160 Reason for Referral 42349-1
31721 Mono-oligo/Di-oligo Ratio 35469-6
31720 A-oligo/Di-oligo Ratio 35475-3
34474 Tri-sialo/Di-oligo Ratio 90420-1
34476 Apo CIII-1/Apo CIII-2 Ratio 90421-9
34475 Apo CIII-0/Apo CIII-2 Ratio 90419-3
50820 Interpretation 53808-2
50822 Reviewed By 18771-6

Clinical Information

Glycosylation is the post-translational modification of proteins and lipids by the addition of glycans (sugars and sugar chains) in a complex stepwise fashion in the endoplasmic reticulum, Golgi apparatus, cytosol and sarcolemmal membrane. Congenital disorders of glycosylation (CDG) are a group of over 150 inherited metabolic disorders characterized by abnormal protein and lipid glycosylation. There are 2 main groups of CDG: type I, characterized by defects in the assembly or transfer of the dolichol-linked glycan in either the cytosol or endoplasmic reticulum (ER) and type II, involving processing defects of the glycan in the ER and Golgi apparatus. In addition, there are 2 categories of glycosylation: N-glycosylation where N-linked glycans are attached to a protein backbone via an asparagine residue on the protein, and O-glycosylation where O-glycans are attached to the hydroxyl group of threonine or serine. Apolipoprotein CIII (Apo-CIII) isoforms, with a single core 1 mucin type O-glycosylate protein, is a complementary evaluation for the CDG type II profile. This analysis will evaluate mucin type O-glycosylation, a defect involving the Golgi apparatus, which is detected biochemically by the change in ratios of the 3 isoforms.


CDG typically present as multi-systemic disorders with a broad clinical spectrum including, but not limited to, developmental delay, hypotonia, with or without neurological abnormalities, abnormal magnetic resonance imaging findings, skin manifestations, and coagulopathy. There is considerable variation in the severity of this group of diseases ranging from a mild presentation in adults and children to severe multi-organ dysfunctions causing infantile lethality. In some subtypes, phosphomannose isomerase-CDG (MPI-CDG or CDG-Ib) in particular, intelligence is not compromised. CDG should be suspected in all patients with neurological abnormalities including developmental delay and seizures, brain abnormalities such as cerebellar atrophy or hypoplasia as well as unexplained liver dysfunction. Abnormal subcutaneous fat distribution and chronic diarrhea each may or may not be present. The differential diagnosis of abnormal transferrin patterns also includes liver disease not related to CDG including galactosemia, hereditary fructose intolerance in acute crisis, and liver disease of unexplained etiology.


Transferrin and apolipoprotein CIII isoform analysis are the initial screening tests for CDG. The results of the transferrin and apolipoprotein CIII isoform analysis should be correlated with the clinical presentation to determine the most appropriate follow-up testing strategy including enzyme, molecular, and research-based testing. Enzymatic analysis for phosphomannomutase and phosphomannose isomerase in leukocytes (PMMIL / Phosphomannomutase and Phosphomannose Isomerase, Leukocytes) should be performed if either PMM2-CDG (CDG-Ia) or MPI-CDG (CDG-Ib) is suspected.


Other glycosylation pathways, in addition to N- and O-glycosylation, have been elucidated, in particular, glycophosphatidylinositol (GPI)-anchored protein glycosylation disorders in which there is absent or decreased expression of all the GPI-linked antigens, and alpha-dystroglycanopathies caused by impaired synthesis of O-mannose glycans. Neither class of disorders are routinely picked up by CDG analysis in serum but are typically diagnosed using molecular methods (CDGGP / Congenital Disorders of Glycosylation Gene Panel, Varies).


Positive test results could be due to a genetic or nongenetic condition; additional confirmatory testing is required.


In serum, the bi-antennary transferrin (di-oligo) fraction is the most abundant transferrin isoform. Congenital disorders of glycosylation (CDG)-I generally show increases in mono-oligo- and/or a-oligo transferrin isoforms whereas CDG-II shows elevated increased transferrin with truncated glycans of varying degree depending on the type of defect.(1)


Results are reported as the mono-oligosaccharide/di-oligosaccharide transferrin ratio, the a-oligosaccharide/di-oligosaccharide transferrin ratio, the tri-sialo/di-oligosaccharide transferrin ratio, and the apolipoprotein CIII-1/apolipoprotein CIII-2 ratio, and the apolipoprotein CIII-0/apolipoprotein CIII-2 ratio. The report will include the quantitative results and an interpretation.


The congenital disorders of glycosylation (CDG) profiles are categorized into 5 types:

1. CDG type I profile. Mono-oligosaccharide/di-oligosaccharide transferrin ratio and/or the a-oligosaccharide/di-oligosaccharide transferrin ratio are abnormal. This group should have the apolipoprotein C-III profile within the normal ranges, because the Golgi system is not affected in CDG type I.

2. CDG type II profile. The tri-sialo/di-oligosaccharide transferrin ratio is abnormal. In this category, the apolipoprotein C-III profile will have 2 scenarios:

A. The apolipoprotein CIII-1/apolipoprotein CIII-2 ratio and/or the apolipoprotein CIII-0/apolipoprotein CIII-2 ratio will be abnormal. In this case, the defect is most likely glycan processing in the Golgi apparatus; therefore, a CDG (conserved oligomeric Golgi [COG]) defect or defect that alters the Golgi apparatus is likely.

B. The apolipoprotein CIII-1/apolipoprotein CIII-2 ratio and/or the apolipoprotein CIII-0/apolipoprotein CIII-2 ratio are normal. In this case, the defects most likely do not involve the Golgi system, thus the molecular defect is different.

3. CDG mixed type profile (type I and II together). In this type of profile one can have abnormal tri-sialo/di-oligosaccharide transferrin ratio with the mono-oligosaccharide/di-oligosaccharide transferrin ratio and/or the a-oligosaccharide/di-oligosaccharide transferrin ratio abnormal and may have the apolipoprotein CIII-1/apolipoprotein CIII-2 ratio and the apolipoprotein CIII-0/apolipoprotein CIII-2 ratio normal or abnormal, depending on if the defects involve Golgi apparatus.

4. CDG with normal transferrin and apolipoprotein profile. Some CDG (eg, PGM3, some ALG13, MOGS, NGLY1, SLC35C1, Fut8) pose a problem for their detection. Thus, a careful medical history, physical exam, and analysis of other protein status may be informative for general protein glycosylation defects. If suspicious for either NGLY1- or MOGS-CDG, specific oligosaccharides in urine can be detected (OLIGU / Oligosaccharide Screen, Random, Urine).

5. When the profile cannot be categorized following the above classification, the abnormalities will be reported descriptively according to the molecular mass of the glycan isoform structures.


Reports of abnormal results will include recommendations for additional biochemical and molecular genetic studies to identify the correct form of CDG more precisely. If applicable, treatment options, the name and telephone number of contacts who may provide studies, and a telephone number for one of the laboratory directors (if the referring physician has additional questions) will be provided.


For more information, see Transferrin and Lipoprotein-CIII Isoform Analysis.

Clinical Reference

1. Lefeber DJ, Morava E, Jaeken J. How to find and diagnose a CDG due to defective N-glycosylation. J Inherit Metab Dis. 2011;34(4):849-852

2. Peanne R, de Lonlay P, Foulquier F, et al. Congenital disorders of glycosylation (CDG): Quo vadis? Eur J Med Genet. 2018;61(11):643-663

3. Freeze HH, Eklund EA, Ng BG, Patterson MC. Neurology of inherited glycosylation disorders. Lancet Neurol. 2012;11(5):453-466

4. Hennet T, Cabalzar J. Congenital disorders of glycosylation: a concise chart of glycocalyx dysfunction. Trends Biochem Sci. 2015;40(7):377-384

5. Freeze HH, Chong JX, Bamshad MJ, Ng BG. Solving glycosylation disorders: fundamental approaches reveal complicated pathways. Am J Hum Genet. 2014;94(2):161-175

6. Sparks SE, Krasnewich DM. Congenital disorders of N-linked glycosylation and multiple pathway overview. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 2005. Updated January 12, 2017. Accessed May 25, 2023. Available at

7. Ng BG, Freeze HH. Human genetic disorders involving glycosylphosphatidylinositol (GPI) anchors and glycosphingolipids (GSL). J Inherit Metab Dis. 2015;38(1):171-178. doi:10.1007/s10545-014-9752-1

8. Bouchet-Seraphin C, Vuillaumier-Barrot S, Seta N. Dystroglycanopathies: About numerous genes involved in glycosylation of one single glycoprotein. J Neuromuscul Dis. 2015;2(1):27-38

Report Available

3 to 6 days

Method Name

Affinity Chromatography-Mass Spectrometry (MS)


1. Congenital Disorders of Glycosylation (CDG, CDGN, OLIGU) Patient Information

2. If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.

Testing Algorithm

Suggested Testing Strategy:




Mayo Test ID

N-glycan, core 1 mucin type O-glycosylation, and conserved oligomeric Golgi (COG) complex defects

Transferrin, apolipoprotein CIII

CDG / Carbohydrate Deficient Transferrin for Congenital Disorders of Glycosylation, Serum

N-glycan, core 1 mucin type O-glycosylation, and COG complex defects

Serum total N-linked glycans, transferrin, and apolipoprotein CIII

CDGN / Congenital Disorders of N-Glycosylation, Serum (includes test ID CDG)

Stepwise analysis of transferrin, apolipoprotein CIII, and serum total N-glycans



CDGGP / Congenital Disorders of Glycosylation Gene Panel, Varies


For more information, see Epilepsy: Unexplained Refractory and/or Familial Testing Algorithm.

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information: